USDM turbo wiring Vs. everything else

[PhyrraM]

On the USDM turbos, post-facelift (maybe 91s also?) there are 3 connectors to the engine. On non-turbos models there are only 2 connectors.

The third connector is only grounds. Any grounds have been removed from the other 2 connectors and placed in the third connector. This makes the USDM turbo intake manifold harness non-plugin compatable with anything else.

Even EJ20Gs only have 2 connectors and route the grounds through them. In fact, other than the extra 2 igition channels, the EJ20G appears to be pin-compatable with non-turbo cars.

Why do you think Subaru did this? A factory "grounding mod" for better signal strength from the sensors? If so, why not the EJ20Gs?

Smog? If so, why only on the turbo? Why not on 49 state cars?

Just wondering. It doesn't really effect my swap, but something I did notice in my research.

[Legacy777]

Actually the 1990 MY n/a legacies and maybe the 1991 MY n/a legacies have a 3-plug engine harness design, however all of their plugs are square.

The turbo legacy harness has 2 square plugs and one round plug.....and as you mentioned the 92-94 legacies have 2 square plugs.

[92 ra-r]

Now that I am going through an EJ20G swap in a 92 SS, I've noticed all the different plugs as well. This being the major thing I've noticed (2 plugs on the G harness and 3 on the SS harness)
For those of you who have swapped the same thing, did you swap the whole engine harness off the 22T (mainly the IM harness) and use all 3 plugs? I can only imagine getting the 20G in and not having grounds, etc from the harness.

What's the best solution here? Swap the 22T harness over, or repin the plugs? I'd kind of like to keep the coil on plugs, but if that won't work, then I'll do waste spark.

I've been searching since 11:30 this morning and this is the only result I've found that mentions the 3 plugs vs 2 plugs!

[PhyrraM]

Swap your USDM intake harness to the ej20g. If your keeping the coil on plugs, then just add the 2 extra wires. You need to extend a few wires anyways (IAC).

Doing it this way sure beats repinning both ends of the harness to match the ej20g manifold harness.

I've got pics of how I did mine, if your interested.